1. Field of the Invention
This invention relates to a via-drilling system and, more particularly, this invention relates to a low-cost, high-throughput drilling system for multi-micro-via-hole arrays, wherein each micro-via-hole is configured as a result of plural controlled applications of energy from sources including at least one patterned high-energy laser beam, resulting in an array of configured micro-via-holes.
2. Description of Related Art
The desire for multi-hole patterns of ultra-miniature via holes, are precisely located and of precise dimensions (multi-micro-via-hole patterns), is recognized in the fields of ink-jet print heads, aerosol generation and micro-filtering. Other, similar desires are expected as well, as other fields become more miniaturized. Miniaturization has far exceeded the capability of the metal drill bit, at least for high-precision via-drilling in tough substrates, because of bit breakage and bending, which not only destroys the drill bit but also destroys the symmetry and precision of the via-hole. Laser drilling is becoming the art of choice for drilling micro-via-holes. However, laser drilling is quite costly, and prior art technologies typically produce via-holes with low aspect ratios (hole depth: hole diameter ofxe2x89xa61:1), or produce imprecise via-hole dimensions. Such laser drilling has exhibited low yields of acceptable multi-micro-via-hole patterns. As miniaturization continues, laser output beams take on the characteristics of shotgun patterns, making an untreated laser beam unsuitable for multi-micro-via-hole-array drilling. A previous patent application, Ser. No. 08/794,217, filed Jan. 29, 1997, HIGH SPEED DRILLING SYSTEM FOR MICRO-VIA PATTERN FORMATION, AND RESULTING STRUCTURE, K. Jain, T. J. Dunn, N. O. Farmiga, C. S. Weisbecker and C. C. Kling, by a set of inventors which includes the inventor in this application, solves the shotgun pattern effect problem and many other problems with a technique involving a laser beam treated by homogenizer and projection optics to achieve an intense, self-luminous small-field image which is configured as a polygon. The substrate is scanned by complementary polygonal scans, through a mask, to ablate the desired via-hole pattern in a plastic ribbon. The previous patent application results in a via hole with entry aperture only somewhat larger than the exit aperture; the via hole is conical in configuration. A separate patent application, Ser. No. 08/889,307, filed Jul. 7, 1997, SIMULTANEOUS, TWO-SIDED PROJECTION LITHOGRAPHY SYSTEM, K. Jain, an inventor of the above patent application, has a technique for laser-imaging both sides of a substrate simultaneously, with registration of topside and bottom patterns. The technologies of these two prior art patent applications are useful in implementing this invention, but do not supply the control of configuration of micro-via-holes which is the subject matter of this invention.
The object of the invention is to control the configuration of micro-via-holes in tough, thin substrates, by controlling partial drilling of micro-via-holes in a first step, and in a subsequent step by controlling patterned, homogenized laser ablation of the finished micro-via-holes within partially drilled holes produced during said first step.
Another object of the invention is to provide a novel laser micro-via-hole drilling system which can contemporaneously drill a large number of configured high-quality via-holes in a selected micro-via-hole array pattern, with exceptional precision, speed and economy.
A feature of the invention is the provision of a beam divider for efficiently separating the laser beam into a number of separate sub-beams for delivery of drilling pulses to top and bottom surfaces of pattern drilling beamlines simultaneously, registered so that the micro-via-hole is not only configured with a selected configuration but passes through the substrate in the selected alignment.
An advantage of the invention is that configured micro-via-holes may be made resistant to blockage by having the exit hole larger than the entry hole.
Another advantage of the invention is that the configuration of micro-via-holes is easily changed, allowing the same xe2x80x9csoft toolingxe2x80x9d equipment to serve in the laboratory by making prototypes, to serve as a pilot system to prove out techniques and product, and then to serve as an easily changed mass production tool xe2x80x94without the cost and risk of investing in special purpose xe2x80x9chard tooling.xe2x80x9d
Still another advantage of the invention is that the precision resulting from the use of masked projection lithography is combined with high-repetition presentation of the substrate for very high-speed, very-high-precision micro-via-pattern drilling at low cost for high production volumes.
Yet another advantage of the invention is that the flow resistance of a micro-nozzle array can be dissociated from the thickness of the substrate by adjusting the relative depths of the cups and of the stems of cup/funnel-configured via holes in the array.
Other objects, features and advantages of the invention will be apparent from the following written description, claims, abstract and the annexed drawings.